SUMMARY: Using the corresponding amino-acid decarboxylases, the six amino-acids arginine, glutamic acid, histidine, lysine, ornithine and tyrosine were found to be free inside the cells of yeast. They are present when growth takes place in the absence of amino-acids, but their concentration may be increased by growing the organisms in media rich in amino-acids. Uptake of glutamic acid from the external medium is dependent on a source of energy which can be provided by the simultaneous fermentation of glucose. The presence of an ammonium salt in the medium decreases both the rate at which glutamic acid enters the cells and the amount of glutamic acid which can be taken up. Certain other amino-acids exert a similar sparing action on the assimilation of glutamic acid, which can be related to their efficiency as nitrogen sources for growth. The free glutamic acid content of cells remains practically constant when the cells are suspended in salt solutions without amino-acids, but if glucose is also present then the concentration of free glutamic acid inside the cells decreases steadily. When ammonia is also present the concentration of glutamic acid remains constant, suggesting that glutamic acid is synthesized by the cells under these conditions, or alternatively that the ammonia is assimilated and utilized preferentially.


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